The present invention relates to a mechanically controlled brake booster, in particular, for automotive vehicles, utilizing the differential of pressure between a partial vacuum and atmospheric pressure and comprising basically a low-pressure casing with at least one movable wall disposed therein and a pressure control valve, the movable wall subdividing the low-pressure casing into a low-pressure chamber and a working chamber and acting upon a push rod guided in an axial direction of the brake booster. In addition to this, a reinforcement tube is provided in the low-pressure casing extending at least approximately in an axial direction connected to the end walls of the low-pressure casing, and in which reinforcement tube a control casing of the pressure control valve is slidably arranged and sealed by means of seals, with a transmission device being fastened to the movable wall and to the control casing to mechanically couple the movable wall to the control casing.
A brake booster of this type has been disclosed in the copending U.S. application of J. Belart and F. Wienecke, Ser. No. 61,113, filed July 26, 1979, assigned to the same assignee as the present application. The movable wall is arranged slidably on the reinforcement tube in this brake booster. The reinforcement tube includes at least two slots extending in a longitudinal direction and receiving slidably therein at least one cross member to mechanically couple the movable wall to the push rod. The cross member, being of U-shaped or T-shaped construction, engages in a groove disposed on the circumferential surface of the control casing or the push rod normal to the longitudinal axis and is rigidly secured to the movable wall. In this brake booster, the movable wall includes a hub extending along the entire length of the slots, with the cross member being secured to the one end of the hub, while its other end is provided with a slide seal.
Although this proposed brake booster operates basically satisfactorily, there are still problems occurring with respect to construction and operation when passing the cross members through the reinforcement tube. In particular, the method of the transmission of force between the movable wall and the control casing results in the overall length of the brake booster being comparatively large, since a seal is not possible at the slots and, thus, the length of the reinforcement tube corresponds to double the power stroke. In addition, the wall thickness required for this transmission of force is comparatively great.